1. Field of the Invention
The present invention relates to a recorder of an ink jet system, and more particularly, it relates to an ink jet recorder having a capping device for an ink jet nozzle.
2. Description of the Background Art
In general, an ink jet recorder comprises a structure which is specific to a system of making recording by jetting ink, in addition to a structure which is directly related to the recording. When the recorder itself is not used for a long time, therefore, ink remaining in a jet nozzle or an ink chamber communicating with the jet nozzle may be thickened due to evaporation of water, leading to incapability of jetting. In order to prevent this, there are provided an ink suction method of sucking the thickened ink from the jet nozzle or the ink chamber for eliminating the same, and a capping device (sealing device) for sealing a jet nozzle surface thereby preventing evaporation of water from the ink through the jet nozzle. While a system of sealing the jet nozzle against the outside air has been employed in general, air may be forced into the ink jet nozzle when the same is capped, to cause defective jetting. In order to prevent this, an additional device is provided for making a cap communicate with the atmosphere immediately before bringing the same into contact with the ink jet surface thereby preventing forcing of air. An example of a conventional jet nozzle sealing device is now described with reference to FIGS. 9, 10 and 11, on the basis of Japanese Patent Laying-Open No. 61-277456 (1986).
Referring to FIG. 11, numeral 101 denotes recording heads, each having a storage part for ink which is supplied from an ink supply source, a passage for jetting the stored ink and an orifice provided on its forward end, and further comprising an energy converter consisting of a piezoelectric element which is one of electromechanical transducers or a heating underflow body which is one of electrothermal converters. For example, four such recording heads 101 are provided for color recording in response to ink colors, while only a single recording head is provided for monochromatic recording. These recording heads 101 are mounted on a carriage 102, which is slidable along two guide shafts 118. The recording heads 101 are connected with the carriage 102 by flexible cables 106, so that control signals for the recording heads 101 are transmitted through the flexible cables 106. The carriage 102 is fixed to an intermediate portion of an endless belt 114, which is driven by a motor 116 to reciprocate the carriage 102. Upper and lower pairs of rollers 110 and 112 are provided in parallel with the guide shafts 118 to be opposed to the carriage 102, and a recording paper P is guided to be held between the respective rollers 110 and 112. A paper feed motor 108 is fixed to an end of one of the rollers 110, for feeding the recording paper P.
On the other hand, a suction recovery device 120 is provided on a home position shown by symbol H. This suction recovery device 120 has a structure shown in FIGS. 9 and 10. The suction recovery device 120 is assembled with reference to a substrate 120a, and a motor 125 is fixed to a part thereof. A pinion gear 125a which is fixed to an output shaft of the motor 125 engages with a gear 125b, while another pinion gear (not shown) which is integrated with the gear 125b engages with another gear 125c. Still another pinion gear 125d which is fixed to a rotary shaft of the gear 125c engages with still another gear 124. Two trapezoidal cams 124a are projectingly provided on an upper surface of the gear 124 to be circumferentially separated from each other at prescribed angular spaces.
On the other hand, a pump lever 129 is pivotally supported by a support frame 129a which is projectingly provided on the substrate 120a through a shaft 129b, to be rotatable along its intermediate portion. An end of the pump lever 129 is provided with a roller 129c to be in contact with upper portions of the cams 124a projectingly provided on the gear 124, while another end thereof is in contact with a piston 126a of a pump 126 through a projection 129d. The piston 126a is regularly urged to project by a spring which is provided in the pump 126, for regularly bringing the roller 129c into contact with the gear 124.
A plurality of caps 122a to 122d which are made of an elastic material such as rubber are fixed to a cap holder 121. The caps 122a to 122d, which are provided with ink absorbers 137 on inner lower portions thereof respectively, are connected to the pump 126 through tubes 127a to 127d independently of each other. The cap holder 121 is slidably provided on the substrate 120a, and regularly pressed by a spring (not shown) to be separated from the pump 126. A gear 123 is rotatably pivotally supported on a lower side of the cap holder 121. An internal cam 123a is formed on an upper surface of the gear 123, so that a shaft 121a projecting from the lower end of the cap holder 121 is in contact with the internal cam 123a through a roller. Therefore, the cap holder 121 is repeatedly pushed back toward the pump 126 by a projecting portion of the cam 123a following rotation of the gear 123. The position of the cap holder 121 is detected by a switch 131.
On the other hand, the respective caps 122a to 122d have vent tubes 128a to 128d, in addition to the ink suction tubes 127a to 127d. End portions of the vent tubes 128a to 128d are connected to an electromagnetic valve device 132. A support frame 133 is fixed in the electromagnetic valve device 132 as shown in FIG. 10, so that the ends of the vent tubes 128a to 128d are connected to the support frame 133 in a side-by-side manner, and opened to the atmosphere. A solenoid 134 is so provided that its rod 134a is directed toward the support frame 133, and a valve 135 is fixed to its forward end for blocking opening ends of the vent tubes 128a to 128d. Numeral 136 denotes a return spring.
The operation of the conventional device having the aforementioned structure is now described. Every opening/closing operation is carried out during single rotation of the gear 124 from a cap open state, i.e., a recordable state with the caps 122a to 122d separated from a nozzle portion of a recording head (not shown). Namely, the gear 123 is rotated once during single rotation of the gear 124, so that substantially all caps 122a to 122d engage with the nozzle portion (are closed) during the rotation and this state is detected by the switch 131 for detecting opening/closing of the caps 122a to 122d. The caps 122a to 122d engage with the nozzle portion in such a state (ventilation state) that the opening ends of the vent tubes 127a to 127d are not blocked by the valve 135 with no operation of the solenoid 134. Then, the solenoid 134 operates to block the opening ends of the vent tubes 128a to 128d, whereby the roller 129c of the pump lever 129 comes into contact with the upper portion of one of the cams 124a by rotation of the gear 124 to rotate the pump lever 129 anticlockwise in FIG. 9, so that the pump 129 carries out a first sucking operation. Then, energization for the solenoid 134 is intercepted so that the valve 135 is retracted to provide a ventilation state. In this state, the roller 129c of the pump lever 129 comes into contact with the upper portion of another cam 124a, so that a second pump sucking operation is carried out. This is the so-called nonprocess suction, for sucking excess ink which is sucked in the caps 122a to 122d toward the pump 126 with air contained in the vent tubes 128a to 128d. During the nonprocess sucking operation, ink which is held by the ink absorbers 137 of the caps 122a to 122d and that adhering to the forward end of the nozzle are also sucked toward the pump 126. An ordinary cap opening/closing operation is automatically carried out through a timer for drying the nozzle portion and preventing sticking of dust, and executed as nonprocess suction in a ventilation state when no recording is made for a constant time.
Also in ordinary employment, the ink may be preliminarily jetted into the caps 122a to 122d when a non-recording state continues for a constant time after the power source is turned on, in order to obtain a proper ink jet state. The caps 122a to 122d stores excess volumes of ink in this case, and hence the ink may adhere to the forward end of the nozzle to result in instable jetting, or the recording paper is contaminated by excess ink dripping on the same when the caps 122a to 122d are opened. In order to prevent this, the aforementioned nonprocess suction is carried out in a ventilation state by an instruction from a control unit (not shown), to stabilize the ink jetting. The caps 122a to 122d are regularly opened/closed in a ventilation state, whereby it is possible to prevent retraction of a meniscus of the nozzle caused by increase of the air pressure in the capping operation.
In the conventional device, however, a mechanism for communication with the atmosphere such as the electromagnetic valve device 132 is provided in the suction recovery device 120 as shown in FIGS. 9 and 10 in order to open a relief valve (atmosphere communication valve) for preventing forcing of air into the ink jet nozzle when the caps 122a to 122d are brought into contact with an ink jet surface. Therefore, the conventional device is complicated in mechanical structure, and inhibited from miniaturization of the overall unit. Further, the conventional device is instable in reliability due to the complicated structure.